Motor speed control



June 20, 1944. G. L. GRUNDMANN MOTOR SPEED CONTROL Filed June 28, 1941 2Sheets-Sheet l ./V. :Snnentor P mhzmLrllndf/za/w Itforneg June 20, 1944.G; GRUNDMANN 2,351,759

MOTOR SPEED CONTROL Filed June 28, 1941 2 Sheets-Sheet 2 'AVATA'A:inventor Gttorneg Patented June 20, 1944 MOTOR SPEED CONTROL Gustave L.Grundmann, Westmont, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application .lune 28, 1941, Serial No. 400,271

(Cl. T28- 5.4)

5 lalms.

invention relates' to motor speed control circuits or systems andparticularly to such control circuits and associated apparatus asapplied to television receivers ior maintaining a color lter disc orwheelv in synchronlsm with a similar color vwheel at the transmitter.

En the post it hos been common practice in television systems tortransmitting color pictures to utilize et both trsnsmitter ond receivercolor lltere, mounted on discs or wheels which are rotated insynchroniser hy means of synchronous motors operated rcm 'o commonepowerline. in systems opersted in this wey the synchronous :motors ore ratherlorge und expensive, this being true even when port of the grower issupplied by i noir-synchronous motor.

As to the use oi s. common power line, this is objectionable hecsuse itmeans that in some lo cslities s color receiver cennot be operated. ifthe synchronizing sewer for the synchronous motors obtained from ocircuit controlled by 'pulses transmitted und cmpliiled suciently todrive the motor. such o circuit is expensive because it must supply siair'ly large amount oi lcower` to the synchronous motor.

in object oi the present invention is to provide an linsisten/ed methodof end means for drivlng color Wheels or the litre in synchronsirn in o.television system.

A further object ol the invention is to provide en improved speedcontrol system Jior television or like apparatus.

A still mtherobject oi the invention is to provide on improved method ofond means :for controlling the speed of e. non-synchronous motor.

l still further object of the invention is to provide en improved methodof and means for controlling the speed of a, split-phase motor of thecapacitor type.

in one oi the preferred embodiments'ol' the invention the color wheel etthe television receiver is driven hy e. split-phase capacitor type motorin which those endsoi the two field wind ings that ordlnarilyareconnected directly together are, instead, connected together through orectifier such as e. diode. As a result, the

` motors capacitor will become fully charged and one neld winding willhave no current ilowing f through it thereafter unless a dischargecircuit is provided for the capacitor. Since the speed of the motordepends upon the amount of current flowing through the said one winding.the motor speed may be' controlled by means of a. vacuum tube in a.capacitor discharge circuit.

Further in accordance with one embodiment of the invention, the requiredsynchronizing control voltege which is to be applied to theabovementioned vacuum tube is obtained by mixing pulses from stone wheelor the like rototing with the color wheel together with pulses from thevertical deilecting circuit. The combined pulses cre rectified andfiltered to produce the desired control voltage `which changes in veluein respouse to any change in the phase relation of the tivo groups oipulses.

ln o preferred embodiment of the invention there is provided, besidesthe above-described control circuit, o circuit which provides ocompa-ran tively rough speed control, this circuit being eiective whenthe speed of the color wheel is too 'Ear from the synchronous speed forthe synchronizing f circuit itself to be effective.

@ther objects, features end advantages of the invention will be apparentfrom the following description taken in connection with the eccompanyingdrawings in which Fig. l is e. block ond circuitdiagram or" s.television receiver to which one embodiment of my invention is applied,

Figs. 2a to '2e are curves which ere referred to in explaining theoperation of the receivers shown in Figs. l end d,

Fig. 3 is c. curve showing the relotion of the motor speed to thecontrol voltage generated by the tone wheel in Fig. l,

Fig. i is o block and circuit diagram showing another embodiment of theinvention applied to a. television receiver,

Fig. o 'is another block ond circuit diagram of s. television receivershowing c. preferred embodiment of the invention, ond Figs.' da und 6b'are curves which are referred to in explaining the operation of thecircuit in Fig. 5.

Referring to Fig. l, the television. receiver is of a well-known typecomprising a iirst detector and s. tunable oscillator indicated at lo,an intermediate frequency amplifier and a second detector indicated atll, a video amplifier i2 and a cathode ray tube i3. The receiver isdesigned for the reception of the usual composite signal comprisingpicture signals end horizontal and vertical synchronizing pulses, ahorizontal synchronizing pulse following each scanning line arid avertical synchronizing pulse occurring at the end of each verticaldellection. v

The said composite signal is supplied both to the cathode ray tube I3and to a. suitable synchronizing pulse separating and ltering circuitindicated at I4. From the circuit I4, horizontal synchronizing pulsesare supplied to a horizontal defiecting circuit I3 and verticalsynchronizing pulses are supplied to a vertical deilecting circuitcomprising the usual blocking oscillator |1 an saw-tooth wave shapingcircuit I8. i

A color wheel 2| is provided for rotating color.

illters past the cathode ray tube |3. In the specic example beingdescribed, there are three color iilters (red, blue and green) on eachhal! oi the wheel 2|, a total of six lters. Also, there are six metallicteeth 22 on the wheel 2|, one for each filter, to form a tone Wheelwhich induces voltage pulses in a pickup coil 23 provided with apermanent magnet to provide the necessary flux. g

The color wheel 2| is driven by a capacitor type split-phase motor 2Boi' conventional design except for the speed control connections. Themotor comprises an amature 21 to which the color wheel 2| is coupledthrough a shaft 28, Ileld windings 23 and 3| which are displaced theusual 90 degrees in space, and a capacitor 32 through which flows thecurrent for the winding 3|.

The winding 23 is connected directly across the 60 cycle power line. Oneend of the winding 3| is connected to one side oi' the power linethrough the capacitor 32 while the other end of this winding isconnected to the other side of theV line through a rectifier such as adiode 33. The last mentioned end of winding 3| in the ordinarysplit-phase motor connection is connected to the other side of the linethrough a direct connection rather than through a rectifier.

It will be apparent that with the motor connections thus far described,the current flow through coil 3| would be only momentary and would stopas soon as the capacitor 32 became fully charged. The motor speed iscontrolled by charge between positive halt cycles of the 60 cyclevoltage applied to the plate of the diode which receives a chargethrough a comparative- 1y high resistance resistor 48 and which isdischarged suddenly through the tube 48. Thus, there is produced asawtooth wave as shown in Fig. 2a which is of suilicient amplitude forcontrol purposes.

f controlling the amount the capacitor 32 can dis- 33, thus controllingthe amount of current flow through winding 3|.

This discharge of capacitor 32 is controlled by a vacuum tube 34 whichmay be a conventional screen grid tube having a cathode 3B, a controlgrid 31, a screen grid 38 and a plate 33. The tube 34 is connectedbetween the diode end of coil 3| and the diode side of the 60 cycle linein such direction that when the half cycles of the 60 cycle supply arenegative at the plate of diode 33, the capacitor 32 may discharge acertain amount through tube 34 depending upon the potential of thecontrol grid 31 with respect to the cathode 38. Wit-h this connection,it will be noted, the tube 34 is connected across the diode 33. Thescreen grid 38 may be connected to the side of the line that is positiveduring the discharge periods for the capacitor 32, or otherwise providedwith a positive operating potential.

The synchronizing control voltage for the grid 31 of tube 34 is obtainedas follows:

The pulses produced by the tone wheel in the i coil 23 are supplied overa conductor 4| to an amplifier 42 and the ampliiled pulses are thenimpressed upon a blocking oscillator 43 oi' conventional design -whichproduces pulses of large amplitude at the tone wheel frequency. Theoscillator 43 is employed merely as a convenient means for converting oramplifying the tone wheel pulses to pulses of the required amplitude.

'I'he blocking oscillator pulses are supplied over a conductor 44 to thedischarge tube 46 of a sawtooth wave generator comprising a condenser 41To the above-described sawtooth wave there is added a. second sawtoothwave occurring synchronously with the vertical deflection. This secondsawtooth wave, which is illustrated in Fig. 2b, is produced in addedrelation to the first wave by means oi.' a discharge tube 5| which hasits plate-cathode impedance connected across the sawtooth condenser 41and its control grid connected to the vertical deilecting oscillator |1i'or the reception of positive pulses. The control grid of tube 5| maybe connected to the grid ci a blocking oscillator, for example.

It will be noted that the condenser 41, the resistor 43 and thedischarge tubes 43 and 3|, in eiect, form two sawtooth wave generatorswhich produce the waves of Figs. 2a and 2b in added relation, the addedor combined waves appearing across the condenser 41 as shown in Figs.2c, 2d and 2e,

The amplitude of the combined waves depends upon the 4phase relation ofthe two sawtooth waves. This is illustrated in Figs. 2c to 2e where thesawtooth waves produced by the tone wheel and by the vertical defiectingoscillator are combined in the different phase relations indicated bythe legends, Fig. 2e representing the condition when the color wheelsawtooth waves are slightly retarded in phase.

The combined waves are applied to a detector tube 52 whereby thereappears in its plate circuit a current flow which varies in accordancewith the phase relation of said waves. This plate current flow isfiltered by a condenser 53 connected across the plate resistor 54 sothat, as applied to the grid 31 of the control tube, it is a D. C.control voltage which varies in accordance with any change in the phaserelation of the vertical deflection and the color wheel rotaion.

As previously explained, an increase in the negative bias on the grid 31of the control tube will permit less discharge of the motor capacitor 32and the motor 26 will slow down. Conversely, a decrease in this negativebias will speed up the motor 2li.

Considering the circuit operation more in detail, the speed of the motor28 is Ilrst adjusted manually, as by means of a variable tap 5E on theVoltage divider 51, so that the color wheel 2| is running in synchronismwith the vertical deiiection when the two sawtooth waves (Figs. 2a and2b) have a. phase relation such as illustrated in Fig. 2e where thecolor wheel sawtooth occurs slightly later than the other sawtooth. Thenthe automatic control action is as follows:

If the motor starts to speed up, the phase relation o! the sawtoothwaves moves towards that shown in Fig. 2c and the amplitude of thecombined wave increases the plate current of tube 52, whereby the plateend of resistor 64 becomes more negative. This increases the negativebias on the grid 31 oi the control tube and the motor 26 is slowed down.

Similarly, if the motor starts to slow down. the phase relation oi thesawtooth waves moves towards -that shown in Fig. 2d whereby theamplitude of the wave applied to the tube 52 decreases, the platecurrent of tube 52 decreases and the grid of tube 31 is made lessnegative so that the asunto motor speeds up. It has been found that thecolor wheel can be held in synchronism in this manner. Y

In Fig. 4, there isshown an embodiment of the invention in which anadditional speed control is combined with a control of theabove-described type. The additional control circuit utilizes a flowthrough the plate resistor 54 varies to change tuned circuit 6l to givea comparatively rough y l control of the motor speed to avoid anydimculty in bringing' the motor to synchronous speed at which time thephase shift operated circuit becomes eiective.

in Fig. fi, the parts corresponding to those in Figure 1 are indicatedby like reference characters.

As shown in Figure a the tone wheel pulses are supplied over theconductor 4l and through an amplifier tube 6G to the tuned circuit 6lwhich is tuned slightly ofi the frequency at which the tone wheel pulsesoccur when the color wheel 2l is in synchronlsm. More specically, thetone Wheel frequency at synchronism is located about heli way down onthe low frequency side o1 the resonance curve of the tuned circuit di,this ad justinent being similar to that commonly usedl in well-irnownautomatic frequency control cir cuits.

Thus, any change in the motor speed will change the voltage across thetuned circuit Bl'. This voltage is applied to an amplifier S2 in thephase control circuit and a diode rectier 63 in the rough speed controlcircuit.

The rectified output from diode 63 is illtered by the RC combination.Sii-S'l and applied to a D. Il amplifier 6d which causes a current flowthrough the plate resistor o'f-l the tube 52. This current now has avalue depending upon the motor speed. Ii the motor speedspup, for e5:-ample, the-output of rectifier 63 increasesF the grid 3l! of the motorspeed control tube 3Q goes more negative, and the motor 2b is sloweddown. ,a reverse action takes place if the motor starts to run too slow.

The above-described tuned circuit type of speed control circuit isrelied upon only to hold the motor close to synchronous speed.

Exact synchronism is maintained by the other portion ci the circuitwhich controls the motor speed in accordance with a phase difference asdescribed in connection with. Figure l. This portion oi the' circuitcomprises a sawtooth wave producing circuit which includes the dischargetube 82 having a plate resistor lll through which a condenser H receivesa charge. The positive halves of the sine wave voltage produced acrossthe tuned circuit Si by the tone Wheel pulses discharge the condenser'li periodically to produce a sawtooth wave.

y to the diodes.

in accordance with any changes in said phase relation, thus holding themotor at synchronous speed.

Referring more specifically to the circuit operation, ifthe motor 26starts to speed up. the phase relation of Figure 2c is approached, theoutput of rectifier 13 increases, the 'negativebias on the grid 31' ofthe motor control tube is in# creased, and the motor slows down.

In Fig. 5 there is shown a speed control and synchronizingcircuitsimilar to that or' Fig. 4, but substantially improved withoutcomplicating the circuit. Specifically, the rough speed con trol portionof the circuit is made substantially independent of line voltagevariations by utilizing a balanced circuit design. As will be explained.below, the synchronizing control (the speed control responsive to phaseshift) is intro:-

duced into the circuit in a simplified manner.

In Fig. 5 the parts corresponding to those vin the preceding gures areindicated by like reiaz erence numerals.

The tone Wheel pulses are applied over the conductor di to a circuitcomprising' amplifier tubes 8l and B2 which have their plate circuitscon-n nected in balanced relation.

The amplified pulses from tubes 8i and B2 are applied to a pair of tunedcircuits u?. and B which are connected'in balanced relation both to thetubes 8l and 82 and to a pairof diode rectiers 86 and 8l. These tunedcircuits are for the saine purpose as the tuned circuit 6i of Fig. thatis, they are so tuned with respect to the tone wheel frequency at colorwheel synchronism that the voltage across them changes with any changein the speed of the color wheel 2i.

Specifically, in the example being described, the circuit 83 is tuned toresonate slightly below the tonewheel frequency at synchronism while thecircuit 84 is tuned to resonate slightly above said frequency. Thus anincrease in the color 'wheel speed will increase the voltage across thediode 8l.

The rectified outputs of the diodes 86 and 8l appear across the loadresistors 88 and 89, .respectively, which are connected infbalancedrelation The load resistors areshunted by filtering condensers 9| and d2and by an output resistor a3 having a variable tap 9d. y

The output of the balanced circuit is applied Y from. the tap St to adirect current amplifier 96 rae discharge tube sa is hem biased beyondlcut-oi between the positive peaks of the sine wave by gridleals biasingasis Well-known in the art.

Pulses from the verticaldeflectina oscillator il cause the tube 5i tofunction as a second discharge tube for the condenser 'il whereby twogroups ci sawtooth waves add to produce a com bined wave having anamplitude dependent upon the phase relation of the two groups of wavesas explained in connection with Figure l..

The said combined voltage `wave is applied to a diode rectifier 13whereby a D. C. control voltage appears across the RC circuit 'I4- 16,this voltage having an amplitude depending upon the above-mentionedphase relation.

The control voltage from rectifier i3 is applied 'to the D. C. amplinertube 52 so that the current 75 whereby the speed control voltage isimpressed upon the grid 3l of the motor control tube 38 as in theembodiment of Fig. e.

The tap et preferably is set at the electrical midpoint of resistor 93so that when the color wheel is at synchronous speed the voltage at 94with respect to the cathode of 4amplifier tube 96 is only the voltagefrom a voltage divider 8l, which voltage appears between the cathode tap9&3 and a variable tap 99. The tap 99 is initially adjusted to make thecolor wheel run approximately at synchronous speed.

From the foregoing it will be apparent that if the color wheel tends torun too fast when power is applied to the receiver, the output of diode8l will increase, the control grid of tube 96 will go less negative andthe grid 31 of motor control tube 34 will go more negative whereby themotor 28 will be slowed down. The opposite action takes place if themotor tends to run too slow.

In order to hold the color wheel in synchronism, rather than merely ataspeed close to lator l1 are impressed upon one of the diodes in .i

the balanced circuit. In the specific example illustrated, positivepulses from the oscillator l1 are applied to a buffer tube Il and, afterbeing reversed in polarity by means of an R-C circuit ill-lill, areimpressed upon the cathode of the diode Il. The R-C circuit may have thecapacity and resistance values indicated on the drawings.

The resulting voltage wave appearing upon the cathode of the diode B8 isshown in Figs. 6a and 6b for two different phase relations of pulsesfrom the vertical deflection oscillator and sine waves produced by thetone wheel in the tuned circuit Il. In Fig. 6a the phase relation is forthe case when the color wheel is in synchronism, the pulse falling onone side of the sine wave and 4with such polarity as to produce a notchtherein.

In Fig. 6b there is shown the phase relation resulting from the colorwheel starting to speed up. Here the notch occurs near the top of thesine wave whereby the amplitude of the notched wave is reduced. Thisresults in a decrease in the output of the diode B6, since it functionssubstantially as a peak rectifier. and its plate goes less negative.This makes the tap 94 more positive withrespect to the junction point ofresistors 8l and 89 (and with respect to the cathode of amplifier 88)whereby the control grid of tube I6 goes more positive (less negative)to increase the negative bias on the grid 31 of the motor control tube34. Thus the motor is caused to slow down. i

From the foregoing it will be apparent that I have provided an improvedmethod and system for holding a motor in synchronism with an incomingsynchronizing signal and that I have also provided a simple andeffective way of controlling the speed of a split-phase motor.

I claim as my invention:

l. In combination, a motor which is to run in synchronism with asynchronizing signal, means actuated by said motor for producing acontrol signal in a fixed time relation to the speed thereof, afrequency responsive circuit to which said control signal is applied,circuit means responsive to a change in the phase relation of twoapplied voltages, means for applying said synchronizing signal and saidcontrol signal to said phase responsive circuit means, and means forcontrolling the speed of said motor in accordance with both saidfrequency responsive means and said phase responsive means.

asume 2. In combination. a motor which is to run in synchronism with asynchronizing signal. means yactuated by said motor for producing acontrol signal as a function of the speed of said motor, a frequencyresponsive circuit to which said control signal is applied, circuitmeans responsive to a change in the phase relation of two appliedvoltages, means for applying said synchronizing signal and said controlsignal to said phase responsive circuit means. and means for controllingthe speed of said motor in accordance with both said frequencyresponsive means and said phase responsive means.

3. In a television receiver, a non-synchronous motor for moving colorfilters successively into position for color picture reproduction, meansactuated by said motor for producing a control signal, means forreceiving a synchronizing signal, control means for producing a, voltageoutput which changes in value in response to a change in the phasedifference of two signals applied thereto, means for'applying saidcontrol signal and said synchronizing signal to said control meanswhereby its voltage output varies with any phase difference between saidsignals, and means for controlling the speed of said motor in accordancei with said voltage output.

4. In combination, a motor which is run in synchronism with asynchronizing signa means actuated by said motor for producing a controlsignal in a fixed time relation to the speed thereof, a balancedfrequency responsive circuit to which said control signal is applied,said balanced circuit including a rectifier, means for applying saidsynchronizing signal to said rectifier whereby its output changes inresponse to either frequency or phase changes of said control signal,and means for controlling the speed of said motor in accordance with theoutput of said balanced circuit.

5. In a television receiver, a split-phase motor for moving colorfilters successively into position for color picture reproduction, saidmotor having two field windings, a capacitor connecting two ends of saidwindings, a rectifier connecting the other ends of said windings, and avariable impedance device connected across said rectifier, meansactuated by said motor for producing a control signal, means forreceiving a synchronizing signal, control means for producing a voltageoutput which changes in value in response to a change in the phasedifference of two signals applied thereto, means for applying Saidcontrol signal and said synchronizing signal to said control meanswhereby its voltage output varies with any phase difference between-saidsignals, and means for controlling the impedance of said variableimpedance device in accordance with said voltage output.

GUSTAVE L. GRUNDMANN.

